1. Field of the Invention
The present invention relates to telephony and, more particularly, to voice over Internet Protocol (VoIP) telephone systems.
2. Related Art
Early in the history of telephony, businesses found that their needs were not fully served by telephone exchanges owned and operated by common carriers. Furthermore, it was overly cumbersome and expensive for businesses to connect each user's telephone to a distinct external telephone line. In response to these problems, businesses have adopted a variety of private telephone systems in an attempt to decrease costs, simplify maintenance, and increase the functionality provided to their users.
For example, a “key system” is a kind of multiline telephone system typically used in small office environments. Each telephone in a key system typically has a set of buttons corresponding to a set of external telephone lines. When an external telephone line is in use by someone in the office, the corresponding button on each phone is lit. To place an external telephone call (i.e., a telephone call over the public telephone network), a user presses the corresponding button on the telephone. Key systems often allow connections to as many as about ten external telephone lines. The ability to switch a larger number of telephones onto a smaller number of telephone lines eliminates the need for each telephone to be connected to a distinct external line. Such systems may provide a limited range of additional features, such as an intraoffice intercom and the ability to place lines “on hold.”
One drawback of key systems is that they require each user to manually select an external telephone line for use. In contrast, a private branch exchange (PBX) system is capable of selecting outgoing lines and performing other switching functions automatically. Users of a PBX system may place internal calls merely by dialing a (typically 3- or 4-digit) extension number. To place an outgoing call, a user simply picks up the telephone handset and dials an external telephone number, possibly prefixed by a code such as the number nine. Most large businesses now use some form of PBX system.
In addition to providing the benefits of allowing a large number of telephones to be switched automatically among a relatively small number of external telephone lines, modern PBX systems typically provide their users with additional features, such as voicemail, call forwarding, call conferencing, and speed dialing.
Some PBX systems now use the Internet Protocol (IP) to carry calls. One benefit of such “voice over IP” (VoIP, or IPBX) systems is their ability to enable voice and data to be transmitted over a single network, thereby creating the opportunity to eliminate the added cost of building and maintaining separate voice and data networks within a company.
In general, a special VoIP-enabled telephone is required to connect to a VoIP network. Alternatively, however, an analog telephony adapter (ATA) may be coupled to a standard analog telephone to enable such a telephone to connect to a VoIP network. Current ATAs typically use the SIP protocol.
VoIP-enabled telephones typically require expensive hardware resources to enable them to communicate using the Internet Protocol. Such phones typically require, for example, a digital signal processor (DSP) or reduced-instruction set computer (RISC), and an Ethernet Media Access Control (MAC) device to support an Ethernet protocol stack. The need to include such components in VoIP-enabled telephones drives up the manufacturing cost of such telephones. Although costs may be reduced by using a key system or by connecting an analog telephone to an IP network using an ATA, such solutions sacrifice the features and scalability that are often desired and even necessary in modern business environments.